UNIVERSITY   OF   CALIFORNIA 

COLLEGE   OF   AGRICULTURE 

AGRICULTURAL   EXPERIMENT   STATION 

BERKELEY,  CALIFORNIA 


POWER  REQUIREMENTS  OF 
ELECTRICALLY  DRIVEN  DAIRY 
MANUFACTURING  EQUIPMENT 


A.  W.  FARRALL 


BULLETIN  433 

September,  1927 


UNIVERSITY  OF  CALIFORNIA  PRINTING  OFFICE 
i  BERKELEY,  CALIFORNIA 

1927 


POWER  REQUIREMENTS  OF  ELECTRICALLY 

DRIVEN  DAIRY  MANUFACTURING 

EQUIPMENT 


A.  W.  FAEEALLi 


INTRODUCTION 

That  the  use  of  electrical  energy  in  dairy  manufacturing  has 
become  general  in  California  is  evident  from  the  fact  that  it  is  used  in 
more  than  900  plants  of  various  sizes  and  types  operated  in  the 
state.  Data  show  that  92  per  cent  of  the  plants  use  electrical  energy 
for  power;  that  the  total  horsepower  of  electric  motors  installed  in 
all  plants  exceeds  73,800;  that  the  annual  power  bill  amounts  to 
approximately  $2,486,000. 

There  has  been  a  considerable  demand  for  information  regarding 
the  energy  requirements  and  load  characteristics  of  dairy  manufac- 
turing equipment,  and  also  regarding  the  energy  requirements  of 
various  manufacturing  processes  in  which  electrical  energy  is  used. 
This  information  is  necessary  as  a  basis  for  improving  the  design  and 
the  operating  efficiency  of  the  machinery,  and  also  as  a  basis  for 
determining  costs  in  cost  accounting.  A  study  has  been  made  by  the 
Division  of  Dairy  Industry  in  which  numerous  laboratory  and  field 
tests  have  been  conducted  and  data  have  been  secured  covering  these 
points,  with  special  reference  to  California  conditions. 


ENERGY  REQUIREMENTS  FOR  DAIRY  MANUFACTURING 
EQUIPMENT 

The  energy  used  in  the  processing  of  dairy  products  is  an  import- 
ant item  in  the  cost  of  manufacture.  The  dairy  plant  operator  who 
keeps  cost  accounting  records  of  this  phase  of  his  business  has  made  a 
step  toward  greater  efficiency.  In  order  to  obtain  the  maximum  value, 
however,  he  must  know  the  actual  amount  of  energy  consumed  by  each 
piece  of  his  equipment  and  compare  its  performance  with  that  of  an 
established  standard. 

One  purpose  of  this  publication  is  to  offer  a  suitable  basis  for 
comparison.  Data  were  secured  covering  the  actual  energy  require- 
ments of  the  more  important  types  of  dairy  manufacturing  equip- 


1  Junior    Agricultural    Engineer,    Divisions    of    Agricultural    Engineering    and 
Dairy  Industry  Cooperating. 


4  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

ment,  when  used  under  normal  conditions  such  as  would  be  found  in 
the  average  dairy  manufacturing  plant. 

A  summary  of  the  data  secured  is  shown  in  Table  1,  which  gives 
the  name  of  the  equipment  used,  the  process  carried  on,  the  product 
treated,  the  rated  capacity  of  the  machine,  the  size  of  motor  used,  the 
unit  of  product  taken  as  a  basis  for  comparison,  and  the  kilowatt 
hours  of  electrical  energy  used  per  unit  of  product  handled.  The 
results  presented  in  this  paper  were  obtained  from  a  large  number  of 
individual  trials  with  each  machine,  and  for  the  most  part  from 
machines  of  average  capacity.  In  making  comparisons  with  equipment 
of  sizes  other  than  those  given,  one  should  remember  that  more  efficient 
results  will  usually  be  obtained  from  larger  equipment,  and  vice  versa. 
The  cost  of  energy  used  in  carrying  on  a  certain  process  may  be 
calculated  as  illustrated  in  the  following  paragraph. 

Problem : 

Find  the  cost  of  electrical  energy  used  in  washing  1000  milk 
cans  in  a  can  washer  of  the  type  using  motor-driven  pumps,  when 
electrical  energy  costs  two  cents  per  kilowatt  hour. 

Solution : 

Referring  to  Table  1,  line  10,  it  is  found  that  the  energy 
requirement  for  this  type  of  washer  is  3.5  kw-hr.  per  100  ten- 
gallon  cans  washed.  The  cost  of  electrical  energy  for  washing 
1000  cans  then,  will  be 

10  X  3.5  X  $0.02  =  $0.70. 

Factors  Affecting  Energy  Consumed. — The  amount  of  energy  used 
by  a  machine  is  affected  by  its  mechanical  condition  and  by  the 
methods  used  in  its  operation.  For  most  economical  results,  all  valves 
and  pistons  must  be  kept  tight  and  the  stuffing  boxes  well  packed,  so 
that  they  neither  bind  nor  leak.  All  bearings  must  be  properly 
adjusted;  the  chains  or  belts  used  must  have  the  proper  tension  and 
alignment,  and  all  moving  surfaces  where  there  is  friction  must  be 
kept  properly  lubricated. 

The  machine  should  be  operated  at  uniform  speed  and  at  as  nearly 
its  rated  capacity  as  possible.  Intermittent  starting  and  stopping  of  a 
machine  or  process  consumes  energy  needlessly.  The  operator  should 
endeavor  to  turn  off  the  power  as  soon  as  the  process  is  completed,  for 
motors  operate  very  inefficiently  at  light  load  and  disturb  the  elec- 
trical balance  of  the  entire  system.  A  large  number  of  motors  run- 
ning idle  may  cause  such  a  low  power  factor2  on  the  system,  as  to 
bring  about  undue  heating  of  those  fully  loaded. 


2  Low  power  factor  increases  the  current  flow  for  a  given  amount  of  energy 
transmitted. 


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b  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

The  size  of  motor  used  should  be  equivalent  to  the  power  require- 
ment of  the  machine  driven  or,  in  order  to  care  for  overloads,  it  may 
be  a  trifle  oversize.  Most  motors  are  made  large  enough  to  carry  a 
momentary  overload  of  100  per  cent.  The  efficiency  of  a  motor  is 
highest  at  or  very  near  its  rated  capacity,  and  drops  off  markedly  at 
loads  below  one-half  or  above  one  and  one-fourth  of  its  rated  horse- 
power. 

In  processes  making  use  of  electric  heaters,  it  is  very  important  to 
have  all  external  heat  radiating  surfaces  well  insulated.  It  is  often 
more  economical  to  use  large  storage  tanks  for  hot  water,  since  a  small 
amount  of  power  used  over  a  longer  period  of  time  lessens  the  cost 
of  electrical  energy  on  account  of  the  lower  power  and  energy  rate. 

OPERATING    CHARACTERISTICS   OF    DAIRY    MANUFACTURING 

EQUIPMENT 

The  information  given  on  the  following  pages  deals  with  the 
operating  characteristics  of  certain  types  of  dairy  equipment.  A 
study  of  these  results  shows  the  factors  that  affect  the  power  con- 
sumption and  general  operating  characteristics  of  each  type  of  equip- 
ment. It  is  especially  important  to  note  how  by  varying  such  factors 
as  head-pressure  of  a  refrigeration  machine  or  the  type  of  ice  cream 
freezer,  the  power  consumption  of  the  process  is  materially  changed. 
It  is  also  of  importance  to  note  how  the  uniformity  of  load  varies  with 
the  different  machines  and  with  various  methods  of  operation.  Uni- 
formity of  load  is  important  from  the  standpoint  of  determining  the 
proper  size  of  motor  to  use  and  in  assisting  to  balance  the  machine. 
An  unbalanced  condition,  which  usually  causes  a  badly  pulsating  load, 
throws  a  severe  strain  upon  all  the  operating  mechanism,  and  there- 
fore should  be  avoided. 

POWER   CONSUMPTION   OF    REFRIGERATION    MACHINERY 

The  variation  in  power  consumption  of  a  twelve-ton,  double-acting, 
compression  type  of  refrigeration  machine,  when  operating  under 
various  head-pressures  is  shown  in  figure  1.  From  an  observation  of 
the  curve,  it  will  be  seen  that  much  more  power  is  required  to  drive 
the  compressor  against  a  head-pressure3  of  200  pounds  per  square 
inch,  than  against  a  pressure  of  150  pounds,  even  though  the  back- 
pressure is  the  same  under  both  conditions. 


-  Head-pressure  (sometimes  called  pressure  on  the  high  side)  is  the  pressure  in 
the  condenser,  against  which  the  compressor  must  pump  the  refrigerating  gas. 


BUL.  433]     ELECTRICALLY  DRIVEN  DAIRY  MANUFACTURING  EQUIPMENT 


22 

a\ 
ao 

19 

18 
17 

150  160  I7D  180  190  230       220 

\-\ead- pressure.  Fbunds  per  squore   inch. 

Fig.  1. — Belation  of  head-pressure  to  power  requirements 
of  refrigeration  machines. 

The  cost  of  energy  per  ton  of  refrigeration 
pressures,  when  electrical  energy  costs  two  cents 
in  Table  2.  A  comparison  of  results  upon  this 
per  ton  to  be  8.8  cents*  greater  when  operating 
pressure  than  when  operating  at  150  pounds. 


From  a  number  of 
actual  observations 
under  the  conditions 
above,  the  power  con- 
sumption has  been 
found  to  increase 
16.2  per  cent,  with  a 
pressure  rise  of  50 
pounds.  This  in- 
creased power  con- 
sumption  is  due  par- 
tially to  increased 
friction  losses  in  the 
equipment,  but  prin- 
cipally to  the  greater 
head  which  must  be 
pumped  against. 

at  the  various  head- 
per  kw-hr.,  is  shown 
basis,  shows  the  cost 
at  200  pounds  head- 


TABLE  2 
Cost  of  Energy  fob  Driving  Refrigeration  Machine  as  Affected  by  Variation 

of  the  Head-pressure 


Head-pressure,  pounds  per  square  inch 

150 

160 

170 

180 

190 

200 

52.4 

54.5 

55.2 

57.0 

59.2 

61  2 

The  yearly  saving  on  the  power  bill  of  a  50-ton  refrigeration 
machine  operating  at  150  pounds  as  compared  to  200  pounds  head- 
pressure  and  with  electric  energy  at  two  cents  per  kw-hr.  may  be 
calculated  as  follows: 

Fifty-ton   machine   operating   for    10    hours   per   day   for 

360  days  7,500  tons  refrigeration 

Cost  per  ton  at  200  pounds  pressure 61.2  cents 

Cost  per  ton  at  150  pounds  pressure  52.4  cents 

Cost  per  year  at  200  pounds  pressure  $4,590 

Cost  per  year  at  150  pounds  3,930 

Saving  per  year   by   operating   at    150    pounds        

head-pressure 


8  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Factors  Affecting  the  Head-pressure. — Several  factors  influence 
the  head  or  condenser-pressure  of  a  refrigeration  machine.  The  most 
important  of  these  are  the  temperature  and  the  amount  of  cooling 
water  supplied  to  the  condenser.  Other  factors  are  the  size  and 
amount  of  cooling  surface,  the  cleanliness  of  the  condenser,  and  the 
presence  of  air  or  inert  gases.  It  is  recommended  that  at  least  two 
gallons  of  water  at  or  below  70  degrees  F.  be  supplied  per  minute,  per 
ton  of  refrigerating  capacity.  In  some  sections  of  the  country  where 
there  is  a  shortage  of  water  or  where  it  must  be  pumped  a  considerable 
distance,  a  cooling  tower  will  be  found  economical.  It  will  reduce  the 
temperature  of  the  water  so  that  it  may  be  used  over  and  over  again. 
The  larger  volume  of  water  which  is  thus  available  for  circulation, 
makes  possible  a  better  heat  transfer  from  the  condenser. 

The  condenser  should  be  large  enough  to  allow  plenty  of  surface 
for  the  cooling  of  the  ammonia.  The  addition  of  more  condenser 
capacity  will  often  pay  for  itself  in  a  short  time,  through  the  reduc- 
tion of  head-pressure  and  the  consequent  saving  of  power.  Since 
condenser  tubes  become  scaled  over,  they  should  be  cleaned  occasion- 
ally. Instances  are  on  record  where  a  thorough  cleaning  with  a  rotary 
tube  cleaner  has  caused  a  drop  of  50  pounds  per  square  inch  head- 
pressure.  # 

1 '  Non-condensible ' H  gases  tend  to  accumulate  in  the  condenser  and 
fill  space  which  should  be  occupied  by  the  refrigerant,  thus  causing  an 
increase  in  the  head-pressure.  Non-condensing  gases  are  removed  by 
frequent  purging,5  or  by  so-called  " non-condensible  gas  removers." 

OPERATING   CHARACTERISTICS  OF   CHURNS 

The  power  characteristics  of  a  common  single-roller  type  churn 
are  illustrated  by  the  typical  curve  shown  in  figure  2.  The  heavy 
curved  line  A  represents  the  average  power  consumed  at  various 
intervals  during  the  churning  operation.  It  drops  somewhat  after 
the  cream  has  been  churned  for  a  few  minutes,  but  rises  again  as  the 
churning  nears  completion.  One  of  the  principal  features  of  figure  2 
is  shown  by  the  shaded  area.  The  extremes  of  this  area  represent  the 
momentary  variation  in  the  pull  on  the  motor,  as  measured  by  an 
indicating  watt-meter.  Twenty-four  minutes  after  starting  the  pull 
varied  from  zero  to  5%  horsepower.  At  one  instant  the  motor  was 
drawing  5%  horsepower  from  the  line  and  at  the  next  was  drawing 
none.       it  is  readily  seen  that  such   an  unbalanced  load  not   only 


4  ''Non-condensible  gases"  are  those  such  as  air,  nitrogen  and  hydrogen,  which 
collect  in  a  refrigeration  plant  and  are  not  condensed  at  the  usual"  operating 
pressures  and  temperatures. 

5  Purging  is  the  operation  of  blowing  off  gases  from  the  condenser. 


BUL.  433]     ELECTRICALLY  DRIVEN  DAIRY  MANUFACTURING  EQUIPMENT        9 

throws  a  severe  strain  upon  the  driving  motor  and  gearing,  but  also 
upon  the  churn  itself.  To  eliminate  this  unsatisfactory  condition, 
designers  of  churns  should  produce  a  better  balanced  and  smoother 
operating  piece  of  equipment.  The  use  of  counterbalances  would  help 
to  make  the  load  more  uniform.  The  average  power  consumption  for 
the  entire  churning  process  is  indicated  by  the  heavy  broken  line 
marked  "average"  in  figure  2.  This  is  the  value  which  should  really 
determine  the  size  of  motor  required,  provided  that  the  momentary 
load  is  never  so  large  as  to  stall  the  motor  or  greatly  reduce  its  speed. 


o 

2 

O 

r 


Average    momentary 
load  during    churning 


Shaded  area  covers  actual 
momentary   power  variation 


12 


£A 


-   36 

Minutes 


4S 


60 


Fig.  2. — Power  consumption  of  a  typical  churn,  showing  variation  during 

the  churning  process. 


OPERATING   CHARACTERISTICS   OF   ICE   CREAM    FREEZERS 

Method  of  Freezing. — The  power  characteristics  of  ice  cream 
freezers  were  found  to  vary  considerably  with  the  different  types  of 
machines,  methods  of  freezing,  and  kinds  of  mixes.  The  data  collected 
show  that  there  can  be  no  general  recommendation  of  a  definite  size 
of  motor  for  all  freezers  of  a  particular  capacity.  It  shows  also  the 
necessity  of  the  operator's  keeping  in  close  touch  with  the  freezing 
process,  and  emphasizes  the  need  for  some  method  of  indicating  to  the 
operator  the  exact  state  of  the  freezing  process  at  all  times. 

The  simplest  method  of  making  ice  cream  is  to  freeze  the  mix  to  a 
given  stiffness  and  then  turn  off  the  freezing  medium  and  whip  until 


10 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


the  desired  amount  of  air  is  incorporated.  Figure  3  shows  the  varia- 
tion in  power  consumed  by  a  standard  40-quart  freezer  with  the 
horizontal  blade-type  of  dasher,  so  operated.  With  this  method  of 
freezing,  it  is  apparent  that  the  power  consumption  of  the  motor 
increases  gradually,  up  to  the  point  X  where  the  freezing  medium  is 
turned  off,  after  which  there  is  a  decrease  down  to  the  point  Y,  where 


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3. — Power  consumption  of  a  40-quart  freezer  when  the  "freeze 
and  whip"  method  of  freezing  is  used. 


the  ice  cream  is  drawn  from  the  freezer.  The  increase  in  the  power 
consumed  is  caused  for  the  most  part  by  the  increasing  stiffness  of  the 
mix  as  it  becomes  colder  and  by  the  increase  in  friction  of  the  driving 
mechanism.  The  two  rates  of  decrease  that  are  shown  are  both  due  to 
lessened  resistance  to  the  rotating  blades  of  the  dasher.  The  first  or 
more  rapid  decrease,  coming  just  after  the  freezing  medium  is  turned 
off,  results  from  the  softening  of  the  frozen  film,  which  the  dasher  has 
been  scraping  from  the  sides  of  the  freezer.     The  further  or  second 


BUL.  433]     ELECTRICALLY  DRIVEN  DAIRY  MANUFACTURING  EQUIPMENT     11 

one,  is  undoubtedly  caused  by  the  thinning  of  the  mix  and  the  incor- 
poration of  air.  Since  there  are  a  number  of  factors  which  affect  the 
shape  of  the  curve,  no  two  freezers,  even  though  they  be  similar,  have 
been  found  to  give  identical  curves.  Some  of  the  influencing  factors 
are :  change  in  composition  of  mix,  brine  temperature,  and  method  of 
homogenization.  One  point  worthy  of  special  note  is  the  effect  of  a 
leaky  brine  valve.  This  will  ordinarily  prevent  the  drop  in  power 
consumption  after  the  freezing  medium  has  apparently  been  turned 
off.    A  leaky  brine  valve  may  usually  be  recognized  by  the  failure  of 


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Fig.  4. — Power  consumption  of  a  40-quart  freezer  when  the  "freezing 
back"  method  of  freezing  is  used. 

the  pointer  of  an  indicating  ammeter  or  watt-meter,  connected  in  the 
motor  circuit,  to  drop  back.  An  exception  to  this  rule  should  be  noted 
in  the  case  of  some  freezers  which  employ  the  squirrel-cage  type  of 
beater  and  in  which  the  power  consumption  does  not  materially 
decrease  after  the  freezing  medium  is  turned  off.  A  second  exception 
is  in  the  case  of  a  freezer  operated  in  such  a  manner  that  the  ice 
cream  is  "whipped"  as  it  is  frozen,  the  freezing  medium  not  being 
turned  off  until  the  freezing  operation  is  finished. 

The  variation  in  power  consumption  of  ice  cream  freezers  when  the 
"freeze-back"  method  was  used,  is  shown  in  figure  4.  The  curve 
with  this  method,  was  similar  to  that  obtained  with  the  first  method 


12 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


described,  until  the  point  was  reached  where  the  cream  would  be 
drawn,  if  the  first  method  of  freezing  were  being  followed.  "With  the 
second  method  however,  the  " whipping"  was  continued,  and  the 
power  consumption  decreased  still  farther  down  to  point  Y,  at  which 
time  the  mix  had  absorbed  more  air  than  was  desired  in  the  finished 
product.  In  order  to  drive  this  excess  air  from  the  mix,  the  freezing 
medium  was  again  turned  on  at  the  point  Y ;  the  frozen  film  was  again 
built  up  on  the  inside  of  the  freezer  barrel  and  the  cream  became 
stiffer.  There  was  an  accompanying  increase  in  the  power  consump- 
tion up  to  the  point  Z,  at  which  time  the  mix  was  drawn  from  the 


L 
Q) 

la 

Du- 
ty 

<0 
L 
O 

X 


/"®              \ 

V<2) 

V- 

<A 

y 

. 

_P 

®L 

/  / 

// 

1/ 

1/ 

8 


16 


80 


aa 


Minutes 


Fig.  5. — Effect  of  stiffness  to  which  ice  cream  is  frozen,  upon  power 
consumed  by  the  freezer  motor. 

freezer.  A  comparison  of  the  two  methods  shows  that  the  former 
places  a  smaller  average  load  on  the  freezer  motor  and  that  a  shorter 
period  of  time  is  required.  The  first  method  is,  therefore,  preferable 
from  the  standpoint  of  economy  of  operation,  both  time  and  energy 
consumed  being  considered. 

Effect  of  Freezing  to  Various  Degrees  of  Stiffness. — Some  plants 
experience  a  considerable  loss  in  quality  of  ice  cream  and  in  time  and 
energy  consumed  because  the  operators  fail  to  control  properly  the 
stiffness  to  which  the  mix  is  frozen  before  it  is  drawn  from  the  freezer. 
Figure  5  presents  graphically  the  effect  upon  the  power  consumption 
of  freezing  to  various  degrees  of  stiffness,  a  standard  40-quart  brine- 


BUL.  433]     ELECTRICALLY  DRIVEN  DAIRY  MANUFACTURING  EQUIPMENT     13 

type  freezer  being  used.  Curve  N  shows  the  power  consumed  while 
freezing  the  mix  to  an  ordinary  consistency.  Curve  M  shows  that 
consumed  while  freezing  to  a  very  stiff  consistency.  It  is  apparent 
that  the  latter  method  required  considerably  more  time,  energy,  and 
power. 

Another  point  to  be  considered  in  each  method  is  that  of  the  peak 
load.  The  peak  load  L  as  shown  by  curve  M  is  very  much  greater 
than  that  shown  by  curve  N  and  emphasizes  the  fact  that  a  greater 
strain  is  placed  upon  the  motor  and  driving  mechanism  as  a  result  of 


L 

Q) 
<0 

L 
O 

X 


X**® 

(^ 

r® 

1© 

®  ®    ®  1 

^        (@) 

s 

10 
Minutes 


15 


e\ 


Fig.  6. — Eelation  of  power  consumption  of  the  freezer  to  the  stage  of 
freezing  process,  with  a  typical  freezer. 

freezing  the  ice  cream  too  stiff.  Curve  M  shows  results  which  might 
be  obtained  should  the  operator  neglect  to  turn  off  the  freezing  medium 
at  the  proper  time.  Under  such  conditions  the  motor  is  likely  to 
"burn  out."  Moreover,  aside  from  the  effect  upon  the  equipment 
itself,  the  product  lacks  uniformity,  a  quality  highly  desirable  in 
ice  cream. 

Effect  of  Stage  of  the  Freezing  Process  Upon  the  Power  Consump- 
tion of  the  Freezer. — The  relation  of  the  power  consumed  by  ice  cream 
freezers  to  the  stage  of  the  freezing  process,  and  especially  to  the 
amount  of  air  contained  in  the  mix  at  different  intervals,  has  received 
the  attention  of  ice  cream  manufacturers  for  some  time,  as  it  offers 


14  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

possibilities  for  the  control  of  the  freezing  process.  The  relationship 
between  the  power  consumption  and  over-run  or  yield  of  a  40-quart 
horizontal  brine-type  freezer  is  shown  in  a  typical  curve,  figure  6. 
Inspection  of  the  curve  shows  that  the  percentage  of  air,  determined 
by  weighing  and  shown  by  the  figures  within  the  circles  gradually 
increased  from  63  to  86  per  cent,  at  the  time  the  freezing  medium  was 
turned  off  at  point  X.  During  this  period,  there  was  also  a  gradual 
increase  in  the  power  consumption.  As  the  point  X  on  the  chart  was 
reached,  the  freezing  medium  was  turned  off  and  the  power  consump- 
tion dropped,  as  was  described  under  "Methods  of  Freezing."  The 
percentage  of  air  absorbed  by  the  ice  cream  increased  as  the  power 
consumption  decreased.  At  point  Y  the  brine  was  again  turned  on  and 
the  result  was  an  increase  in  the  power  consumption  with  a  correspond- 
ing decrease  in  the  amount  of  air  held  in  the  mix.  The  ice  cream  could 
have  been  drawn  from  the  freezer  at  either  of  the  two  points  A  or  Z, 
each  of  which  shows  an  over-run  of  106  per  cent.  There  would  have 
been  a  slight  difference  in  the  air  content  of  the  drawn  product,  how- 
ever, because  of  the  fact  that  at  point  A  the  air  content  was  increasing, 
while  at  point  Z  it  was  decreasing. 

Among  the  other  factors  affecting  this  relationship  between  the 
power  consumed  and  the  stage  of  the  freezing  process  are  composition 
of  mix,  temperature  of  brine,  and  type  of  freezer. 

The  Effect  of  the  Kind  of  Ice  Cream  Frozen  Upon  Power  Consump- 
tion of  the  Freezer. — Freezing  various  kinds  of  ice  cream  seems  to 
make  a  difference  in  the  power  consumption  of  freezers.  Table  3  shows 
results  obtained  from  the  study  of  the  operation  of  a  40-quart  standard 
dasher,  horizontal,  brine-type  of  freezer,  operating  under  regular 
commercial  conditions,  and  using  the  "freeze  back"6  method  of  freez- 
ing. The  conditions  were  all  comparable  as  to  brine  temperature, 
speed  of  dasher,  and  amount  of  mix.  The  plain  vanilla  ice  cream 
required  the  least  amount  of  time,  or  16.8  minutes,  while  the  straw- 
berry was  next  with  22.1  minutes.  The  chocolate  required  the  most 
time,  with  29  minutes.  It  should  be  mentioned  in  this  connection  that 
the  time  required  for  the  chocolate  ice  cream  could  have  been  reduced 
somewhat  by  cooling  the  syrup  to  a  lower  temperature  before  adding 
it  to  the  mix.  This  is  an  important  point  in  the  manufacture  of  any 
ice  cream,  in  which  a  part  of  the  ingredients  are  added  to  the  main 
batch  during  the  freezing  process,  as  the  addition  of  a  warm  syrup, 
for  instance,  causes  a  breaking  down  of  some  of  the  air  cells,  with  a 
consequent  loss  of  time  in  freezing.  Results  show  a  longer  than 
average  time-requirement,  which  was  due  to  the  small  volume  of  brine 

o  See  page  11. 


BUL,  433]     ELECTRICALLY  DRIVEN  DAIRY   MANUFACTURING  EQUIPMENT     15 

available  for  this  particular  installation,  and  to  the  use  of  the  ' '  freeze- 
back"  method  of  freezing. 

The  average  power  required  during  the  freezing  process  was  1521 
watts  for  the  vanila  ice  cream,  1682  watts  for  the  chocolate,  and  1767 
watts  for  the  strawberry.  Although  the  maximum  power  consumption 
was  about  the  same  for  each  kind,  the  average  was  higher  for  the 

TABLE  3 

Effect  of  Kind  of  Ice  Cream  upon  Power  Consumption  of  the  Freezer 


Kind  of  ice  cream 

Minutes  to 
freeze 

Average 
watts 

Maximum 
watts 

Kw-hr.  per 

10  gallons  of 

ice  cream 

16.8 
29.0 
22.1 

1521 
1628 
1767 

2260 
2408 

2284 

.4258 

.8120 

.6508 

*  Freezing  time  was  slightly  high  on  account  of  small  volume  of  brine  available  in  this  particular 
plant  and  the  use  of  the  "freeze  back"  method  of  freezing. 

strawberry  and  chocolate  because  of  the  longer  period  of  whipping 
after  the  mix  was  partly  frozen.  The  freezing  of  puddings  requires 
considerably  more  power  than  either  chocolate  or  strawberry  ice  cream 
because  of  the  greater  stiffness  of  the  mix. 

The  energy  consumption  per  batch  was  .4258  kw-hr.  for  the  vanilla 
ice  cream,  .6508  kw-hr.  for  the  strawberry,  and  .8120  kw-hr.  for  the 
chocolate. 

Variation  in  the  Power  Required  to  Drive  Different  Freezers. — A 
number  of  factors  enter  into  the  design  of  the  freezer  itself,  all  of 
which  affect  its  power  consumption.  Among  the  most  important  of 
these  are  the  speed  and  type  of  dasher.  Table  4  shows  results  obtained 
from  two  commercial  machines  of  40  quarts  capacity  operating  under 
similar  conditions.  The  first  machine,  which  was  of  the  vertical  type, 
was  driven  at  a  speed  of  225  r.p.m.,  and  used  what  is  known  as  the 
squirrel-cage  type  of  dasher,  in  which  the  rotating  element  carries  a 


TABLE  4 

Variation  in  the  Power  Required  to  Drive   Different   Types   of   Freezers 


Kind  of  dasher 

Speed  of 
dasher, 
r.p.m. 

Temper- 
ature of 
brine,  °F. 

Time  for 
freezing, 
minutes 

Average 

watts 
consumec 

Maximum 

watts 
consumet 

Kw-hr. 

per  10 
gallons  ol 
ice  cream 

Aver- 
age 
H.P. 

Size 
motor, 
HP. 

High  speed   vertical 

225 
165 

6° 
6° 

12.8 
12.3 

2454 

f 
1360.8 

3480 
1982 

.522 
.279 

3.28 
1.83 

3 

Horizontal,     blade- 
and-paddle 

3 

16 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


number  of  rods  held  together  in  the  form  of  the  traditional  squirrel 
cage.  The  second,  which  was  of  the  horizontal  type,  was  driven  at  a 
speed  of  165  r.p.m.  and  was  equipped  with  a  blade-and-paddle  type  of 
dasher.  Both  machines  used  the  same  brine  and  mix,  and  were 
operated  simultaneously.  The  first  machine  used  almost  twice  as  much 
energy  per  batch  of  cream  frozen  as  did  the  second.  The  time  required 
for  each  was  practically  the  same,  being  one-half  minute  less  for  the 


Minutes 

Fig.  7. — Effect  upon  power  consumption  of  adding  ingredients  to  the  mix 
during  the  freezing  process. 

horizontal  standard-blade  machine.  These  data  show  that  the  com- 
mercial type  freezers  of  the  same  capacity  vary  greatly  in  the  power 
required  to  operate  them,  and  that  no  specified  size  of  motor  can  be 
recommended  as  best  for  all  makes  and  types. 

Effect  of  Addition  of  Ingredients  to  Mix  upon  the  Power  Con- 
sumption of  the  Freezer. — It  is  desirable  in  the  freezing  of  certain 
types  of  ice  cream,  such  as  strawberry,  chocolate,  or  puddings,  to  add 
a  part  of  the  ingredients  to  the  mix  after  the  mix  is  partly  frozen. 
This  affects  the  power  consumption  in  several  respects.  First,  if  the 
ingredient  added  is  cold  and  viscous,  it  will  momentarily  increase  the 
power  consumption,  and  also  the  total  energy  consumed  per  batch. 
This  accounts  in  part  for  the  higher  energy  requirement  for  freezing 


BUL.  433]     ELECTRICALLY  DRIVEN  DAIRY  .MANUFACTURING  EQUIPMENT     17 

such  ice  creams.  This  condition  is  illustrated  in  figure  7,  in  which 
the  rise  C-D  in  curve  B  was  caused  by  the  addition  of  a  thick,  cold, 
syrup.  The  third  rise  in  this  curve  resulted  when  the  brine  was 
turned  on.  Curve  A  shows  the  shape  of  the  curve  when  no  ingredient 
was  added  during  the  freezing  process,  other  conditions  being  similar. 
If  the  ingredient  is  hot  or  warm  when  added,  as  is  sometimes  the 
case  in  the  manufacture  of  chocolate  ice  cream,  the  power  consump- 
tion may  drop  momentarily,  on  account  of  a  thinning  of  the  mix  from 
the  heat  absorbed.     This  is  undesirable,  as  was  heretofore  explained. 


L3 
Q) 

o 

V) 

o 

X 


*' 


1000  2000  3000 

Pounds   per  square  inch 


AOOQ 


Fig.  8. — Eelation  of  operating  pressure  to  power  requirements  of  a 
typical  homogenizer. 


OPERATING    CHARACTERISTICS    OF    HOMOGENIZERS 

The  power  consumption  of  homogenizers  varied  almost  directly 
with  changes  of  pressure  at  which  the  machine  operated.  Figure  8 
shows  the  variation  in  the  power  consumption  of  a  100-gallon-per-hour 
homogenizer,  equipped  with  a  5-horsepower  motor  and  operated  at 
constant  speed  and  capacity.  The  power  consumption  increased  in 
direct  proportion  to  the  increase  in  pressure  on  the  homogenizer.  The 
amount  of  power  used  was  the  same,  whether  ice  cream  mix  or  water 
was  passed  through  the  homogenizer.  It  is  evident  that  the  power 
consumption  could  be  taken  as  an  index  of  the  pressure  at  which  the 
machine  is  working.  Variations  of  the  flow  of  the  mix  through  the 
^"mogenizer,  due  to  poorly  fitting  or  leaky  valves  may  be  detected  by 
the  vibration  of  the  power  indicator  needle. 


18 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


OPERATING  CHARACTERISTICS  OF  ELECTRIC  DAIRY  STERILIZERS 

The  common  type  of  electric  dairy  sterilizer  used  mostly  for 
sterilizing  milk  pails,  milking  machine  parts,  and  other  similar  equip- 
ment is  also  used  to  some  extent  in  small  creameries  and  ice  cream 
plants. 

The  apparatus,  as  usually  constructed,  consists  of  an  inclosed  tank, 
in  which  a  small  amount  of  water  is  placed,  and  an  electric  heating 
element  of  from  three  to  five  kilowatt  capacity,  laid  in  or  attached  to 
the  bottom  in  such  a  manner  that  the  water  surrounds  the  heating 
element.     When  the  current  is  turned  on,  the  water  is  heated  and 

TABLE  5 
Operating  Characteristics  of  Dairy  Farm  Sterilizers 


Description  of  sterilizer 

Water 
used, 
pounds 

Minutes 
reach 
170°  F. 

Minutes 
reach 
210°  F. 

Minutes 
above 
170°  F. 

Watts 
demand 

Kw-hr. 

per 
batch 

Cost  to  heat 

sterilizer  to 

210°  F.  at 

2.5  cents  per 

kw-hr. 

5-kilowatt  heater,  uninsulated 

5-kilowatt  heater,  uninsulated 

5-kilowatt  heater,  uninsulated 

5-kilowatt  heater,  insulated  bot- 

50 
17 
10 

17 

17 
17 

17 

26.50 
14.12 
11.30 

13.46 

13.80 
29.22 

29.00 

36.50 
24.64 
22.50 

23.83 

21.78 
54.10 

46.70 

32.50 
22.11 
21.42 

28.00 

33.13 
42.51 

47.07 

5736 
5716 
5607 

5614 

5557 
2883 

2941 

3.48 
2.35 
2.10 

2.23 

2.02 
2.60 

2.29 

8.7 

5.87 

5.25 

5  57 

5-kilowatt  heater,  insulated  bot- 

5  05 

3-kilowatt  heater,  plain  top 

3-kilowatt  heater,  insulated  bot- 

6.50 
5.73 

steam  generated.  The  steam  rises  and  envelops  the  utensils  to  be 
sterilized,  which  are  contained  in  the  tank.  Practical  sterilization  is 
accomplished  by  holding  the  equipment  at  a  temperature  of  210°  F. 
for  fifteen  or  twenty  minutes,  but  satisfactory  results  can  often  be 
secured  by  heating  to  a  temperature  of  170°  F.  for  fifteen  minutes,  the 
minimum  specified  in  the  California  dairy  law. 

The  effect  of  the  amount  of  water,  the  size  of  heater,  and  the 
quality  of  insulation  upon  the  operating  characteristics  are  shown 
briefly  in  Table  5.  A  comparison  of  lines  1,  2,  and  3,  shows  that  the 
energy  consumed  per  batch  was  reduced  from  3.48  kw-hr.  to  2.10 
kw-hr.  by  using  only  ten  pounds  of  water  instead  of  fifty  in  the 
sterilizer ;  that  at  the  same  time  there  was  a  corresponding  decrease  of 
15.2  minutes  in  the  time  required' to  reach  170  degrees  F. 

The  effect  of  insulation  is  evident  from  a  comparison  of  lines  2  and 
5,   which   refer   to   data   obtained   from   uninsulated   and   insulated 


BUL.  433]     ELECTRICALLY  DRIVEN  DAIRY  MANUFACTURING  EQUIPMENT     19 

sterilizers  of  four-can  capacity,  each  being  equipped  with  a  5-kilowatt 
heater.  The  energy  consumption  was  reduced  by  the  use  of  insulation 
from  2.35  kw-hr.  to  2.02  kw-hr.  per  batch.  One  of  the  most  important 
advantages  of  insulation  is  apparent  in  line  five,  which  shows  the 
time  during  which  the  sterilizer  temperature  was  above  170  degrees  F. 
This  was  33.11  minutes  for  the  insulated  sterilizer  and  22.11  minutes 
for  the  uninsulated  one,  the  power  being  turned  off  in  each  case,  at  the 
time  the  temperature  reached  210  degrees  F.  and  the  cover  remaining 
in  place.  The  advantage  of  using  a  large  heating  element  is  shown  in 
lines  5  and  7.  The  5-kilowatt  heater  required  21.78  minutes  as  com- 
pared with  46.7  minutes  for  the  3-kilowatt  one,  under  similar  condi- 
tions. The  energy  consumed  per  batch  sterilized  was  2.02  kw-hr.  and 
2.29  kw-hr.,  respectively.  It  is  evident  that  the  5-kilowatt  heater  gave 
sufficient  heat  to  care  for  the  extra  requirement  during  cold  weather. 
An  automatic  thermostate  is  a  very  desirable  accessory  for  use  with 
electric  sterilizers,  as  its  use  makes  certain  that  the  correct  tempera- 
ture is  reached  and  maintained  for  the  proper  length  of  time.  It  also 
serves  as  a  protection  to  the  heating  element,  in  case  the  operator 
should  neglect  to  turn  off  the  power,  and  it  saves  on  the  cost  of  energy, 
since  it  turns  off  the  power  automatically  as  soon  as  the  required 
temperature  is  reached. 


SUMMARY 

1.  The  electrical  energy  consumed  by  dairy  manufacturing  equip- 
ment may  be  determined  by  the  use  of  suitable  instruments,  and  from 
the  data  secured,  the  cost  of  energy  used  in  the  processing  of  dairy 
products  may  be  accurately  calculated. 

2.  Increased  efficiency  of  operation  may  be  brought  about  by  a 
thorough  study  of  the  power  requirement  of  a  process  such  as  the 
freezing  of  ice  cream  and  by  an  elimination  of  those  conditions  which 
cause  loss  of  power  and  energy. 

3.  A  basis  for  comparison,  as  for  instance,  the  energy  consumed 
per  hundred  gallons  of  milk  pasteurized,  together  with  a  standard  of 
operation,  which  sets  a  certain  number  of  kilowatt-hours  per  unit  of 
product  treated,  is  useful  in  analyzing  and  comparing  the  cost  of 
operation  of  equipment. 

4.  The  power  requirements  and  energy  consumption  of  a  machine 
are  largely  affected  by  conditions  under  the  control  of  the  operator. 
Careful  attention  to  maintaining  the  equipment  in  good  condition, 
operating  it  to  capacity  and  using  proper  methods,  will  give  most 
efficient  results. 


20  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

5. -Careful  selection  of  the  proper  size  and  type  of  equipment  is 
important,  if  best  results  are  to  be  secured. 

6.  In  the  operation  of  a  medium  size  refrigeration  machine  under 
normal  conditions,  a  saving  of  16  per  cent  in  the  cost  of  power  may  be 
expected,  when  the  head-pressure  is  maintained  at  150  pounds  instead 
of  200  pounds  per  square  inch. 

7.  The  proper  balancing  of  such  equipment  as  churns,  will  reduce 
strains  in  the  motor  and  driving  mechanism  and  will  result  in  more 
economical  operation. 

8.  No  definite  size  of  motor  can  be  recommended  for  all  types  of 
ice  cream  freezers,  as  a  large  variation  in  power  consumption  is  found 
with  the  different  types  as  well  as  with  various  methods  of  freezing 
and  kinds  of  ice  cream  manufactured. 

9.  The  stiffness  to  which  ice  cream  is  frozen  should  be  closely  con- 
trolled in  order  to  prevent  overloads  upon  the  motor  and  driving 
mechanism,  to  reduce  the  cost  of  operation,  and  to  secure  uniformity 
of  product. 

10.  The  relationship  between  the  power  consumption  of  the  freezer 
motor  and  the  stage  of  the  freezing  process  is  very  close  with  many 
types  of  freezers.  It  differs  in  individual  machines  and  is  affected- 
somewhat  by  variations  in  kind  of  mix,  age  of  mix,  ingredients  of  mix, 
and  brine  temperature. 

11.  Electrically  heated  dairy  sterilizers  are  practical  and  eco- 
nomical if  properly  designed  and  operated.  The  sterilizer  should  be 
safe  to  operate  when  a  small  amount  of  water  is  used.  For  best  results 
it  should  be  insulated  with  a  double-walled  air  space  and  be  equipped 
with  a  reliable  thermostat  or  time  switch. 


ACKNOWLEDGMENTS 

The  author  wishes  to  acknowledge  the  assistance  given  by  Professor 
C.  L.  Roadhouse  and  Professor  G.  D.  Turnbow  in  the  work  with  ice 
cream  freezers ;  also  that  given  by  Professor  B.  D.  Moses  and  Mr.  T.  A. 
Wood  in  the  work  with  electric  dairy  sterilizers.  Thanks  are  due  the 
Crescent  Creamery  Company  of  Los  Angeles,  The  Los  Angeles  Cream- 
ery Company  of  Los  Angeles,  the  Capitol  Dairy  of  Sacramento,  and 
to  many  other  concerns,  whose  cooperation  made  possible  the  gathering 
of  the  data  for  this  bulletin. 


lOm-9,'27 


